Conventionally, various methods have been used as manufacturing methods of a molding, where an injection molding method, an extrusion molding method, etc. are known. Recently, as a molding molded by such molding methods, a molding containing a thermoplastic resin with a high content of filler mixed therein has been introduced. For instance, there is known a fuel cell separator containing a thermoplastic resin with a filler such as graphite carbon and carbon fiber mixed therein.
The fuel cell separator is disposed so as to sandwich a solid electrolyte and an air electrode and a fuel electrode arranged on both sides of the solid electrolyte in a fuel cell. The air (oxygen) and a fuel gas (hydrogen) are respectively fed to the air electrode and the fuel electrode through grooves formed on the fuel cell separator.
When a molding is formed of a material containing a high content of filler as the fuel cell separator, fluidity of the material is degraded, so that a filling pressure of the material needs to be increased to perform molding.
Then, there has been proposed a molding method such as an injection compression molding method and a rapid heating/cooling method for molding using such materials with low fluidity (see, for instance, Patent Document 1).
However, in the injection compression molding method disclosed in Reference 1, which uses a molding machine with a gate for injecting a melted resin being fixed, it has been difficult to secure uniformity of thickness of a product when a resin composition containing a high content of carbon filler and having extremely low fluidity is molded. Also, in the rapid heating/cooling method in which a die is heated to a high temperature to smoothly fill a resin, it has taken time to raise a die temperature, undesirably causing degradation of productivity with a long molding cycle.
Especially, several hundreds of the fuel cell separators are used in the fuel cell and uniformity of dimensional accuracy is important (in an example of a required performance, variation of thickness (difference between maximum value and minimum value) is desired to be 60 μm or less).
There has also been proposed another method in which a cavity of a die or a gate is slid to shorten an apparent moving distance of a melted resin composition in the cavity in order to obtain a thin molding with a uniformed property. For instance, a material molding method has been proposed, where a traveling piece having a material injection port is provided on either a fixed retainer plate or a movable retainer plate, so that the material injection port is displaced relative to a cavity surface in a filling process of a molding material (see, for instance, Patent Document 2).
Further, there has been another resin molding method in which, when a melted resin is injected into a cavity from a gate through a resin injection port and a running section, the melted resin is injected while relatively moving the gate and the cavity (see, for instance, Patent Document 3).
Patent Document 1: Pamphlet of International Publication No. WO02/001660
Patent Document 2: JP-A 6-179228
Patent Document 3: JP-A-8-150644